A two-cycle engine (also referred to as a “two-stroke engine”) is a reciprocating engine in which intake, compression, combustion, and exhaust strokes make one cycle whenever a piston reciprocates once within a cylinder. The two-cycle engine generally includes a fuel injection port such as an injector within the cylinder and injects a fuel into a combustion chamber in a state of closing a scavenging port and an exhaust port, thereby preventing blow-by of the fuel.
As such a two-cycle engine, a two-cycle reformed gas engine disclosed in the following Patent Document 1 is known. The two-cycle engine is a uniflow type two-cycle engine which includes an exhaust port and a scavenging port at respective upper and lower portions of a cylinder. The two-cycle engine also injects a reformed gas into a combustion chamber during a compression stroke in which the combustion chamber is closed by a piston positioned further upward than the scavenging port after the completion of exhaust.
The uniflow type two-cycle engine of the related art will be described in detail with reference to FIGS. 7 and 8. FIG. 7 is a view illustrating a schematic configuration at the time of a scavenging stroke in the two-cycle engine according to the related example. FIG. 8 is a view illustrating a schematic configuration at the time of gas combustion (explosion) in the two-cycle engine according to the related example. A flammable gas may be used as a main fuel of the two-cycle engine. The following description of the related art will be given of a case of using LNG (Liquefied Natural Gas) as the main fuel of the flammable gas.
The two-cycle engine includes a tubular cylinder liner 4b, a housing 10 which engages a stepped portion on an outer periphery of the cylinder liner 4b to a central opening portion of an upper wall 2a and retains the cylinder liner 4b, a scavenging chamber 12 which is mounted in an opening portion 2b open to the right side in the figure of the housing 10, and a hollow cylinder head 4a mounted on an upper surface of the cylinder liner 4b. Furthermore, the two-cycle engine includes an exhaust valve cage 55 which is mounted to a central opening portion of the cylinder head 4a from above.
A cylindrical piston 3 is vertically movably fitted to a hollow portion (inner periphery) of the cylinder liner 4b. The piston 3 is retained in the cylinder liner 4b and the housing 10 by retaining a piston rod 70 extending downward in a stuffing box 80 which is mounted at a center of a flange portion 2c provided at the inner side beneath the housing 10. A plurality of scavenging ports 9 is formed on side walls of the cylinder liner 4b while facing a space 11 leading to the opening portion 2b of the housing 10. The scavenging ports 9 permit air to be introduced from the space 11 of the housing 10 into the cylinder liner 4b in a state in which the piston 3 is at a bottom dead center as shown in FIG. 7.
The cylinder head 4a is installed with a fuel injection port 13 and a pilot injection valve 5 which are obliquely directed to each other toward a combustion chamber 100 formed in a lower portion of the cylinder head 4a. The exhaust valve cage 55 is formed with an exhaust port 6 which is obliquely directed upward from the bottom open to the combustion chamber 100. In addition, the exhaust valve cage 55 includes an exhaust valve spindle 140 which has an exhaust valve 7 at a lower end portion thereof and is axially supported to be vertically movable. The exhaust valve 7 opens and closes the combustion chamber 100 and the exhaust port 6. The exhaust valve spindle 140 is vertically moved by an exhaust valve drive unit 8, and opens and closes the combustion chamber 100 and the exhaust port 6 by the exhaust valve 7.
As shown in FIG. 8, the fuel injection port 13 is connected with an LNG tank 160 via a high pressure pump 170, an evaporator 180, and a pressure regulating valve 19. The high pressure pump 170 is driven by an electric motor 20. In addition, the pilot injection valve 5 is connected to a fuel injection pump 21.
Next, an operation of the two-cycle engine having such a configuration will be described.
Air supplied from the scavenging chamber 12 is introduced from the space 11 of the housing 10 into the cylinder liner 4b in a state in which the piston 3 is at the bottom dead center at the time of the scavenging stroke shown in FIG. 7. In addition, a combustion gas remaining in the combustion chamber 100 is exhausted from the exhaust port 6 of the exhaust valve cage 55 to the outside during an open state of the exhaust valve 7 at the same time. Thereafter, when the piston 3 is raised (moves toward the combustion chamber 100) in the cylinder liner 4b and the exhaust valve 7 becomes a closed state, the air introduced into the cylinder liner 4b is compressed.
FIG. 8 illustrates a state in which the piston 3 reaches up to a top dead center and the air is compressed to the maximum. In this state, after LNG supplied from the LNG tank 160 is pressured using the high pressure pump 170 driven by the electric motor 20 and is gasified by the evaporator 180, the LNG is injected from the fuel injection port 13 into the combustion chamber 100 while the pressure of the LNG is regulated by the pressure regulating valve 19.
At the same time, a liquid fuel supplied from a liquid fuel tank (not shown) is supplied to the pilot injection valve 5 by the fuel injection pump 21 and injected from the pilot injection valve 5 toward the combustion chamber 100. The liquid fuel self-ignites within the combustion chamber 100 and this flame allows the high pressure LNG injected into the combustion chamber 100 to ignite (explode). By this explosive power (pressure), the piston 3 falls (moves toward the bottom dead center) at high speed in the cylinder liner 4b. Thus, it becomes a state shown in FIG. 7.
Meanwhile, as the arts related to the above two-cycle engine, there are techniques described in Patent Documents 2 and 3 in addition to Patent Document 1.